It takes a bold soothsayer to proclaim that Monday’s men’s final at the United States Open between Kei Nishikori of Japan and Marin Cilic of Croatia represents the end of the oligarchical tennis era ruled by the so-called Big 4.

Novak Djokovic, after all, remains No. 1 in the rankings and won Wimbledon in grand style in July. Roger Federer, even at age 33, is still elegant and eager. Rafael Nadal, who missed the Open with a sore wrist, has not lost his wicked forehand and stout heart. Andy Murray, for all his self-criticism and recent struggles, retains his deft touch and sprinter’s speed.

But Monday’s final — between the 10th-seeded Nishikori and the 14th-seeded Cilic — is certainly an excellent glimpse of what the more egalitarian future of the tennis world could look like. And for those who have followed and worked in the sport for years, it is an unsettling moment to realize that none of the astonishingly reliable stars who have redefined the game in the last decade will be on the court with a Grand Slam trophy at stake.

“There’s no doubt it’s startling, but it’s exciting as well,” said Justin Gimelstob, the former player who is now a television analyst and a member of the ATP Tour’s board of directors. “One of the best things the top players have done for the sport is being consistently excellent, and one of the big challenges they’ve created is that they’ve been so dominant by hoarding the big titles and the limelight that it’s made it hard for others to make a name for themselves.”

The last time there was a Grand Slam men’s singles final without Federer, Nadal, Djokovic or Murray was at the 2005 Australian Open when Marat Safin beat Lleyton Hewitt and that was only after Safin saved a match point against Federer in a titanic semifinal.

But there has been a transitional feel to the 2014 season, beginning early with the Swiss veteran Stan Wawrinka’s surprise Australian Open win in January.

Wawrinka, however, is 29. In Nishikori, who is 24, and Cilic, who is 25, the U.S. Open has two first-time Grand Slam finalists who are truly from the new wave. That is certainly encouraging news to Japanese and Croatian tennis fans but much less of a felicitous development for American television network CBS as it bids farewell to the Open after 46 years without an established figure to anchor its final broadcast.

“Maybe it validates them not paying so much money to keep it,” Gimelstob said of CBS, which will be supplanted by ESPN next year. “Sure, it’s not their dream final. But what are the options? They can look back or look forward and promote the match as it is, promote the talent. Both Cilic and Nishikori outplayed their opponents. Cilic beat Federer. Nishikori beat Djokovic.”

Life after the Big 4 has been a talking point in tennis board rooms for years but is now a focal point. Ask Chris Kermode, the Briton who is in his first year as executive chairman of the ATP Tour.

“When I started in January, I was very conscious at some point I was going to be in the crossroads with the sort of new generation guys breaking through,” he said in a telephone interview. “Every single sporting generation faces this in any sport. When I grew up in the McEnroe, Borg era everyone said that’s the end of tennis. And of course it never is. There is always someone coming through.”

The ATP has started promoting the new wave that includes Nishikori as the “young guns.” But not all eras are created equal, and Kermode said that “commercial revenues for the ATP have grown 200 percent since 2009” on the strength of the Big 4’s collective pull.

Tennis’s strength is that it is a global sport, which can also appear to make it a zero-sum game: One country’s stock rises while another’s falls (see the current world rankings of the once-dominant American men). But in commercial terms, a new star’s nationality is also a major factor. Cilic, a Croatian, comes from a tiny market. Nishikori, the first Asian man to reach a Grand Slam singles final, comes from a major market and even before this run he ranked on the short list just behind the Big 4 in off-court earnings in the men’s game.

“I would say he was probably No. 5,” said Fernando Soler, the global head of IMG Tennis, the company that has long managed Nishikori and in anticipation of his rise has long worked with the Japan Tennis Association. “Kei’s success will have ramifications for all aspects of tennis in the country, which is good because there will be new money coming to tennis.”

His timing is also excellent with the 2020 Summer Olympics in Tokyo and companies, both in Japan and abroad, looking to link sponsorship deals with the Games. Now for the bad, short-term news: The U.S. Open men’s final is scheduled to start at 6 a.m. in Japan and is being broadcast in Japan by Wowow, which is a pay television channel with limited reach.

It is also questionable whether Nishikori’s success will translate into growing the sport in Asia, a vast region that is too often viewed as a whole by outsiders despite its diversity and tense, intracontinental rivalries.

“The fact a French guy wins Wimbledon wouldn’t necessarily change things in Germany,” Soler said. “But what is true is that in Asia there are not many tennis stars besides Li Na, and successes like Kei’s do make the sport more familiar in the entire region. I don’t think it’s going to have a huge impact in Asia, but I’m convinced that it’s going to help in a way to prove to these guys they can play tennis and win.”

The grail from a marketer’s perspective thus remains the emergence of a world-beating Chinese or Indian man: a prospect that for now is only a project.

Craig Tiley, the Australian Open tournament director who was once a collegiate coach in the United States, is an outspoken critic of the sport’s conservative streak and believes it has squandered some of the golden opportunity presented by the long-running success of the Big 4.

“I believe the evidence has shown that tennis has lost ground in attracting youth and lost ground to action sports,” Tiley said. “We are a tradition sport, and we tend to behave very traditionally and are not responsive enough to changing consumer needs.”

Tiley has commissioned global research in the last three years, and said the findings indicate that the four Grand Slam tournaments remain disproportionately strong in terms of generating public recognition and interest and that the sport should be experimenting with shorter, faster-paced formats to attract youth and audiences in emerging markets.

Kermode agrees that length can be a challenge for younger fans and that it is often a sport one “comes to later” as a spectator.

“For me, the issue is getting kids to experience tennis and to play tennis,” he said in a telephone interview. “To sit and watch is quite a tough ask.”

But if they were not patient enough to watch in the age of Federer, it truly will be tough to capture them in the age of lesser champions and, perhaps more important, lesser rivalries.

“Will we see the level of consistency that we’ve seen with these top four playing for grand slams and our own tour’s biggest titles?” Gimelstob said. “Probably not. But that’s unfair to ask, unfair to assume it can be maintained. But the convergence with this new generation challenging the old can also be exciting. And one thing’s for sure: The Big 4 have been dominant for so long, it’s not sneaking up on us.”

A version of this article appears in print on , Section D, Page 9 of the New York edition with the headline: Tennis World Wobbles as Competitive Axis Begins to Shift. Order Reprints | Today’s Paper | Subscribe